PW3 Cam timing

'Cdo's like most Brit bikes are pretty decent off pavement.'
Hobot, I cannot reconcile my mind about the weigfht distribution of a commando used on dirt. I've ridden speedway sidecars a few times, and my mates ride Speedway Jawas. It is always a balance between slide and drive. I think there is also a problem with the torque characterrstics of the motor. The bike was developed for the bitumen, it is probably a bit much to expect it to be good on dirt. I believe the only successful four stroke Brit MX bike was the Clewstroker BSA based bike, built by Jeff Clew and we are talking about obsolete technology there.

Hm, I'm not what I'd call a off road racer even though the loose stuff taught me how to handle tarmac in similar fashion, breaking loose just enough to flick a better aim w/o drifting and sliding like the side cars and flat trackers, though the side car method of steering into the turn is what I do most when loose. By decent I mean the Triumph and Cdo handle the loose rough stuff pasture to Gravel better than my SV650 with suspension modified for off road. Its hard to discuss but in general terms as each turn has its own conditions to dice it nicely. I do now and then put Trixie into weaving wobble by giving tire spin increasing power as soon as I begin a lean, to point the spin helps induce the lean then its exactly like you see the rain racers do or long fast dry slides, crossed up balancing the forward thrust with the lean and rear angle out to resist the outward slide away from direction intended. Its takes over 50-60 to have energy enough to do this w/o hanging up for sudden spills, so got to be a bit crazy mood and I can't stay on it to 80's on Trixie like I could Peel, which is only conditions I could induce something that might be called weave/Hinge but it did not escalate like Trixie so only reason I didn't go faster on Peel was this is public traveled paths into blinds and must ALWAYS be well out of the way on the berm edge of path anytime I can't see very far ahead.

I HATE THE Gravel as I nor any one can really conquer it every time all the time and any time can take ya down, especially when thinking you are taking it easy as can be SPLAT. One most impressive things about my two Cdo is the climb out of river valley - 1/4 mile 30-40 degrees. They can hook up more than my mudder ice spiked posti tract 4wd 4:11 pumpkins PU which can hit 65 but Cdo can touch over 70 before frantic slowing for sharp 100' turn at top and ugh bottom. I could only get upper 50's on soft race compound tires which hook up better than any groove tire, just like tarmac, but something about the power pulses and frame resonance plays back to rear patch to end up just spining to get any more bite upward. I do not know if the blown engine will allow much play getting to tarmac, but got crash cage so will find out one way or another.

One thing I've learned is bikes transition in and out of counter and straight steer and if rear stepping out or grabbing bite again. Depending on lean angle extra power can lift you up or trip you down w/o loosing rear grip. Going up, power tends to lift bike, going down it tends to trip lower. I don't think there's much left for me to learn on pavement after what Peels allowed, oh sure flying her higher and further side ways faster with the launch power of new engine but I'll never get THE Gravel down pat or ways it can take me down.

A lot of modern MotoGP riders have come off the dirt. You often see them putting a foot towards the ground as the y approach corners. It is probably not bad training for modern motorcycles where the tyres hang on forever these days. Riders of much older bikes have usually had the experience of the old compound tyres which would drop you in a flash if you had a hesitant thought . The young guys these days have the luxury of being able to be heavy handed right up until the tyre lets go, after that is when the dirt riding experience would help. It certainly gave Kenny Roberts the edge in Europe. I think the change in riding styles is a result of the changing technology. Have a look at a lot of the old road race videos, you will never see a rider put a foot down when approaching a corner.

That foot/leg out has been the subject of a lot of discussion, and is still undecided.?

It is only on the gearlever side ?
Initially, the commentary was that it was cramp, and they were stretching their leg.

And since seems to have become fashionable....

Rohan said:

That foot/leg out has been the subject of a lot of discussion, and is still undecided.?

It is only on the gearlever side ?
Initially, the commentary was that it was cramp, and they were stretching their leg.

And since seems to have become fashionable....

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+1

acotrel said:

Rohan, It IS weird cam timing, and all I can suggest is that it might be worth somebody trying to duplicate using a similar two into one pipe. I use zero setting clearances, and my figures can be out by 3 degrees.
My current timings are as follows :

Inlet opens 65 BTDC
Inlet closes 59 ABDC
Exhaust opens 94 BBDC
Exhaust closes 27 ATDC

With the combat cam this will be

Inlet opens 65 BTDC
Inlet closes 83 ABDC
Exhaust opens 94 BBDC
Exhaust closes 54 ATDC

I don't believe you could use those exhaust opening points with separate pipes. I've never believed in the commando motor, however I can only say I'm really impressed with mine. It's a big adrenalin rush - a serious bit of gear.

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This is 6 degrees advance over the workshop manual spec. What was the result after advancing? Asking because I have a Norris RX installed in my combat motor. Today was the first time I've had a chance to open it up and it is reluctant to pull passed 80mph. I set it to Norris spec 54BTDC open and 82ABDC close Intake and 82BBDC open and 54ATDC close exhaust. I'm thinking I need to advance a few degrees.

I think a lot depends on the length of the tail pipe. My feeling is that the advanced exhaust timing compensates for the increased gas inertia/back pressure. And the earlier inlet opening lets the motor take a bigger gulp of mixture . I've never used separate pipes on my 850, and if I did, I would use the timings specified by the cam manufacturer. You really know when my motor is running, it bellows but delivers really good power, with no boot in the backside from a cam spot, although I probably never ride it slowly enough to feel one if it was there. All I can say is to try it, check clearances though. My camshaft sprocket has 3 keyways broached at random, to get the timings. Good luck, I hope it works rea lly well for you.

acotrel said:

I think a lot depends on the length of the tail pipe. My feeling is that the advanced exhaust timing compensates for the increased gas inertia/back pressure. And the earlier inlet opening lets the motor take a bigger gulp of mixture . I've never used separate pipes on my 850, and if I did, I would use the timings specified by the cam manufacturer. You really know when my motor is running, it bellows but delivers really good power, with no boot in the backside from a cam spot, although I probably never ride it slowly enough to feel one if it was there. All I can say is to try it, check clearances though. My camshaft sprocket has 3 keyways broached at random, to get the timings. Good luck, I hope it works rea lly well for you.

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This is helpful, thanks. I'm going to check again my cam timing to make sure it is where Norris specifies. My feeling is cam timing. If that doesn't fix the problem will look into changing to a double S combat cam as I'm pretty sure I can set it to the dot mark alignment and it will work. Not racing, just want a street combat that has expected output.

I would always put a degree disc on the motor. I never trust the marks. If you get the timing wrong, the bike can be really poor. There is enough information to let you know what works well. I only play with the timing on my own bike to get the very best performance out of it. You obviously don't need to do that with a road bike, but it still needs to be pretty right. You should not be afraid t o use the degree disc and dial micrometer, it is not rocket science. If you get the timing pretty spot on, you will probably love your commando a lot more. A good hot cam in a motor set to the right timings can give you a beautiful adrenalin rush. My 850 is a real hoot to ride, I love it. 'Some things are so bad, that they are good' !

The CR with cam profile mostly determines what timing the thing likes per octane and that is best determined in a road bike by careful initial time adv till kicker back fire detected then retard til it just don't, them measure any way or make up some numbers but better mark that tedious found setting with razor edge. When timing optimal the thermal stain band on electrode hook will be just before the bend begins. The hotter faster burn more powerful the combo the less advance needed for best combustion torque pressure,till rather high for our engines rpm when it needs some retard to has a chance to be burning well just after TDC. Ignition timing is the first thing to dial in before AnyThing Else or else ...

I've just notice my thread has re-appeared near the top of the list. It seems to have been way off piste for a while now, still, all interesting stuff, ish.

The factory time scale has been reported by some to be up to 12' off but more common a few degree's while some like me had clutch and or crank nut come off to wipe off the whole scale so nothing but by guess and by golly diddle till perfect on limits timing to then put a time light on to see the real objective scale i put on the mag rotor by degree wheel. Easiest way I've found to mount the 'wheel was by super magnets, one on crank end and one holding wire pointer on barrel. If ya like Norton grunting torque rise its most pleasurable tire wasting to set just sort of back fire starts and hi load hi heat hi throttle hi times mature detonation.

In my young stupid days in '99, 3 wks after the time trial wheelie took out R knee, while out of saddle I put on the Boyer that came with the Combat and set by back fire feel and was able to use shattered fractured knee to start ok, then decided better set it more correctly by time light to 32' total ... for a back fire that re-fractured dislocated knee while lifting me off straddling bike to ground in screaming white washed steps on worm for 10 min or so but then eased up and I could gimp ok again then re set back and put light on it to see 28" then learned that was Combat correct ugh. Right now Trixie Combat is on 29' points and only run 87 octane any more w/o an issue i can detect.

Going by collected reports a decade+ now plus my own thrills I think the best there is for real life thrill times a is a good ole bad reputation 2S cam and bigger carbs to feed its breathing up high.

About ignition timing . On everey fourstroke that my brother and I use for racing , if it is on petrol we use the maker specified ignition timing . If it is on methanol we increase the advance by about 4 degrees. We then tune the carburation with those settings fixed. On two strokes on methanol, we usually use the ignition advance specified for petrol in a road motor. If we are using petrol in a two stroke race motor, the specified ignition advance for a road motor, needs to be retarded. In Yamaha aircooled twins, an RD probably uses 2.8mm BTDC advance, a TZ uses 1.8mm advance. One thing we never do is adjust the ignition advance, and the carburation at the same time. Only change one thing at a time. Changing the ignition advance often gives the same symptoms as changing carburation. I suggest that fitting a two into one exhaust on a commando also needs a rethink, and start tuning again.

Tri-Y headers are famous for helping V8 torque when two opposite firing pistons exhale through the same Y, such as our 360' twins. I don't understand the reason for larger exit pipe after the Y as its still only flowing the exhaust pulse of one jug at a time in our twins. I'll be buying a cheap ish wire welder to make up various combos of pipe lengths and diameters til best kick in the seat. Might put in a spring loaded flapper valve for low throttle response in over my cammed engine.

I would have thought the same thing about the tail pipe diameter. A smaller diameter pipe might work on a commando. My 500cc Ttriumph had an extremely top end motor, and the first two into one that I made killed it stone dead. I had a long taper megaphone straight after the collector, and the junction of the two was about one and a quarter times the size of one of the header pipes. I started cutting the collector and the megaphone back and fitting parallel pieces between the two to increase the diameter. The bike was slow until I effectively reached the total crossectional area of the two header pipes. With my Norton 850 engine, I went straight there . The triumph was much better with the two into one, it became quite sane and stopped trying to kill me. And the Norton is really great.
My mate had my Seeley frame before I built my 850 engine into it. He had a Laverda 750 motor in it, and I once raced against the bike when it was fitted with a two into one pipe with a small outlet collector and tail pipe. My Triumph 500 was all over it.
When I made the two into one exhaust for my 850, I used a bit of judgement about lengths, diameters and cam timing , however I still believe 'arse beats class'. My header pipes are the same lengths and diameters as used on a four into one exhaust for a Z1 Kawasaki. My mate used to make them in his business, and that is where I scrounged the bits.

Of course you realise all this tuning stuff is 'secret men's business' ? - that is a joke , and I often say that to my wife when I've fixed something, especially if she asks how I did it . A few years ago the South Australian Government wanted to build a bridge to an island at the mouth of the Murray River. The aborigines were protesting that their old tribal lands were being violated, and one of the things said in court was that the area was a 'sacred site', it was used for 'secret women's business' before the white man came along. Any oblique reference to that will usually provoke an abusive response from our wives , they are a 'mite tetchie'.

On the subject of camshaft timing....need some advise how others are attaching the large degree wheel to the crankshaft drive side. I'm just checking cam timing so don't want to remove the alternator rotor/stator. Primary cover off of course.

Thanks

This is really testing my memory, but I think I once did it by using a rubber expansion plug from the local hardware store. It was just the right size to fit inside the sleeve nut that holds the alternator on. I think I had to make a stepped washer to reduce the size of the hole in my degree wheel to take the smaller stud on the plug.

Ken

I don't have that problem. I've turned d own the bit of the shaft where the rotor use to fit, threaded it and fitted a big nut to hold the sprocket carrier on. I'm using single row chain with Jawa speedway sprockets on a splined carrier because I don't use the commando clutch - the sprocket floats about 8mm. The clutch is an old racing item off a manx.
I note that in one of Hobot's posts , he mentioned that Dyno Dave achieved just under 50 BHP from a commando. I'm wondering what a really quick one turns out ? My chains last a while, but they are a bit of an expense. My bike feels like it is turning out more than 60BHP, however I wouldn't have a clue. As long as it gets with the fast guys, I can do something about outriding them. It seems to be able to do that, and the last time I raced it I was up with them.

lcrken said:

This is really testing my memory, but I think I once did it by using a rubber expansion plug from the local hardware store. It was just the right size to fit inside the sleeve nut that holds the alternator on. I think I had to make a stepped washer to reduce the size of the hole in my degree wheel to take the smaller stud on the plug.

Ken

Click to expand...

This is one of the thoughts I had. Didn't know where to find the rubber plug.

Thanks